Method of producing semiconductor substrate having an SOI structure

ABSTRACT

There is provided a method for suppressing the occurrence of defects such as voids or blisters even in the laminated wafer having an oxide film of a thickness thinner than the conventional one, wherein hydrogen ions are implanted into a wafer for active layer having an oxide film of not more than 50 nm in thickness to form a hydrogen ion implanted layer, and ions other than hydrogen are implanted up to a position that a depth from the surface side the hydrogen ion implantation is shallower than the hydrogen ion implanted layer, and the wafer for active layer is laminated onto a wafer for support substrate through the oxide film, and then the wafer for active layer is exfoliated at the hydrogen ion implanted layer.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 11/796,005 filed Apr. 25,2007. The entire disclosure of the prior application, application Ser.No. 11/796,005 is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of producing a semiconductorsubstrate through a lamination process, and more particularly to amethod of producing a semiconductor substrate through a laminationprocess at a state that a thickness of a buried oxide film is thin.

2. Description of Related Art

Recently, semiconductor substrates having a SOI structure that siliconlayer or so-called SOI layer is formed on an oxide film are applied as awafer for a high-performance LSI in electron devices because they areadaptable for speeding up the device and are low in the powerconsumption and excellent in the pressure resistance, resistance toenvironment and the like.

As the production method of the semiconductor substrate, there are knowna so-called SIMOX method wherein a silicon wafer is implanted withoxygen ions at a high concentration and then subjected to a heattreatment at a high temperature to form an oxide film therein, and amethod called as a so-called lamination process. In the laminationprocess, an oxide film is formed on at least one of a wafer for anactive layer forming SOI layer and a wafer for a support substrate andboth the wafers are laminated to each other through the oxide film andthereafter the wafer for the active layer is thinned to produce asemiconductor substrate in which SOI layer is formed on the buried oxidefilm as an insulating film.

Further, the lamination process can be classified into a grind polishingmethod, a PACE (Plasma Assisted Chemical Etching) method, an ionimplantation exfoliation method (which is called as Smart Cut(registered trademark) method), an ELTRAN method and so on. Among them,the ion implantation exfoliation method is frequently used because thecrystallinity of the active layer and the thickness uniformity of theactive layer are good and the good surface flatness is obtained.

The production procedure of the semiconductor substrate through thelamination process is shown in FIG. 1. That is, a wafer 1 for an activelayer and a wafer 2 for a support substrate are previously provided(step (a)), and an oxide film 3 is formed on at least one of both thewafers (the wafer 1 for the active layer in the illustrated embodiment)(step (b)), and then hydrogen ions (or inert gas ions) are implantedinto the wafer 1 for the active layer to form an ion implanted layer 4in the interior of the wafer 1 for the active layer (step (c)).Thereafter, the ion implanted face of the wafer 1 for the active layeris laminated onto the wafer 2 for the support substrate through theoxide film 3 (step (d)), and subjected to an exfoliation heat treatmentto partly exfoliate the wafer 1 for the active layer at the ionimplanted layer as a cleavage face (exfoliation face) (step (e)), andthereafter re-oxidation treatment is conducted for removing a damagedlayer formed on the surface of the active layer (step (f)), and then theplanarization treatment is conducted through a step (g) of removing theresulting oxide film to produce a semiconductor substrate 7 in which asilicon layer 6 is formed on a buried oxide film 5.

Lately, it is required to produce SOI wafers having a higher quality inassociation with the high integration of the semiconductor devices. Forthis end, it is increasingly demanded to make the thickness of theburied oxide film thinner, for example, up to a thickness of about 20nm, or to directly laminate the silicon wafers to each other withoututilizing the oxide film as to the laminated wafer.

When the laminated wafer is produced by thinning the buried oxide filmor without forming the oxide film through the ion implantationexfoliation process, the wafer for the active layer and the wafer forthe support substrate are laminated to each other by thinning the oxidefilm to be formed on either of the wafers or without forming the oxidefilm.

In the production of the laminated wafer having a thin oxide filminclusive of the case that the buried oxide film is not formed, however,when the exfoliation heat treatment is carried out after the lamination,blisters are generated between the wafer for the support substrate andthe oxide film, or there are generated voids extending from the oxidefilm to the active layer.

That is, in the conventional production of the semiconductor substratethrough the lamination process, defects such as blisters or voids may becaused at the laminated interface. Particularly, such blister or voiddefects tend to frequently occur as the thickness of the buried oxidefilm existing between two semiconductor wafers becomes thinner, whichcomes into a serious problem in the production of the laminatedsemiconductor substrate having a thin oxide film or having no oxidefilm.

As a countermeasure on the frequent occurrence of blisters or voids whenthe thickness of the buried oxide film existing between the twosemiconductor wafers is made thinner, JP-A-2004-259970 proposes that thethickness of the wafer for the active layer is increased to increase thethickness of the active layer to thereby raise the hardness of theactive layer.

However, even when the thickness of the active layer is made thick, ifthe thickness of the buried oxide film is thin, the blisters or voidsoccur naturally. Also, when the thinning of the active layer ispromoted, the thickness of the active layer is thickened at the midwaystep for the purpose of raising the hardness, which takes a great laborin the subsequent thinning treatment and causes the deterioration of thequality. That is, when the thickness of the active layer at the midwaystep is thick, it is required to conduct the thinning of the activelayer by a treatment of thermal oxidation+removal of oxide film, or bygrinding or polishing treatment for obtaining a final desired thicknessof the active layer. In the latter case, as the treating quantity(oxidation quantity, etching quantity, grinding or polishing quantity)increases, the thickness uniformity of the active layer is deteriorated.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide a method forsuppressing the occurrence of defects such as voids or blisters even inthe production of the laminated wafer having a thickness of an oxidefilm thinner than that of the conventional oxide film.

The inventors have made various studies on the frequent occurrence ofthe defect such as voids or blisters when the thickness of the oxidefilm is thin in the production of the laminated wafer and found thefollowing knowledge.

That is, the voids or blisters are generated due to the fact thathydrogen ions implanted into the active layer are diffused into thelaminated interface in the exfoliation heat treatment to form hydrogengas, which weakens the bonding strength between the wafer for the activelayer and the wafer for the support substrate. If the oxide film formedin the wafer for the active layer is thick, the implantation energy inthe hydrogen ion implantation becomes large, so that there is caused aphenomenon that hydrogen ions sputter oxygen from the oxide film andhence oxygen is implanted into the active layer.

When the wafer for the active layer is laminated to the wafer for thesupport substrate and then subjected to the exfoliation heat treatment,it has newly been revealed that oxygen implanted in the active layertraps hydrogen ions to suppress the diffusion of hydrogen into thelaminated interface and hence the generation of defects such as voids orblisters. Further, it has been revealed that when a proper amount ofoxygen is implanted into the active layer, the wafer for the activelayer becomes hard, which contributes to suppress the generation of thevoids or blisters.

On the contrary, when the oxide film formed on the wafer for the activelayer is made thin for thinning the thickness of the buried oxide film,or when the thickness of the oxide film to be formed is made thin at thestep (b) of FIG. 1, the concentration of oxygen sputtered by hydrogenion implantation at the subsequent step (c) and implanted into theactive layer becomes small and hence the diffusion of hydrogen can notbe controlled in the exfoliation heat treatment and the defects such asvoids or blisters are generated.

Based on the above knowledge, the inventors have made variousinvestigations on a method capable of implanting a proper dose of oxygeninto the active layer even when the thickness of the oxide film is madesmall.

At first, the inventors introduced the following equation (I) in theexamination on the above effect of suppressing the hydrogen diffusion byoxygen every factor:N _(D) =N _(HO) +N _(IO) +N _(ID)  (I)where N_(D): total factor number producing the effect of suppressinghydrogen diffusion,

N_(HO): oxygen introduced into active layer through hydrogen ionimplantation,

N_(IO): oxygen introduced into active layer through ion implantationother than hydrogen,

N_(ID): defects introduced into active layer through ion implantationother than hydrogen.

Based on the above equation (I), the inventors have made various casesand sought optimum conditions for avoiding the defects in case that thethickness of the oxide film is thinned.

Firstly, when hydrogen ions are implanted at an implantation energy: 50keV and a dose: 6×10⁶ atoms/cm² into a wafer for an active layer havingan oxide film of usual thickness: 150 nm as the conventional method, agood product having no defect is N_(HO)=4.2×10¹⁴ atoms/cm² from data ofa secondary ion mass spectrometry (SIMS). Also, since ions other thanhydrogen are not implanted, N_(IO)=0 and N_(ID)=0, so that it issufficient to be N_(D)>4.2×10¹⁴ atoms/cm².

Then, it is considered that the condition for obtaining the good productthrough only the hydrogen ion implantation is satisfied in case ofchanging the thickness of the oxide film.

When the condition is N_(HO)=D_(H)(hydrogen dose)×t_(box)(thickness ofoxide film)×k_(HO)(coefficient) . . . (II), from N_(HO)=4.2×10¹⁴atoms/cm², D_(H)=6×10¹⁶ atoms/cm² and t_(box)=150 nm isk_(HO)=4.2×10¹⁴/{(6×10¹⁶)×(150×10⁻⁷)}=4.67×10² (/cm).

From the above equation (II), a relation between D_(H) (hydrogen dose)and t_(box) (thickness of oxide film) isD_(H)=A·1/t_(box)A=N_(HO)/k_(HO).

The results of the relation arranged by D_(H) and t_(box) are shown inFIG. 2. In this figure, when the relation exceeds the upper limit of thehydrogen dose, the self-exfoliation occurs, while when it is less thanthe lower limit, the exfoliation is not caused by the heat treatment, sothat it is assumed that the hydrogen dose is set between the upper limitand the lower limit.

In the light of the above relation, if it is intended to thin the oxidefilm to not more than 50 nm, it is difficult to satisfy N_(D) only bythe hydrogen ion implantation as shown in FIG. 2.

In order to satisfy N_(D), therefore, it has been found that it isnecessary to supplement a portion not satisfied by the hydrogen ionimplantation through an implantation of ions other than hydrogen, and asa result, the invention has been accomplished.

That is, the summary of the invention is as follows.

(1) A method of producing a semiconductor substrate, which comprises thesteps of forming an oxide film having a thickness of not more than 50 nmon a wafer for an active layer forming a silicon layer, implantinghydrogen ions into the wafer for the active layer to form a hydrogen ionimplanted layer, implanting ions other than hydrogen to a position thata depth from the surface side the hydrogen ion implantation is shallowerthan the hydrogen ion implanted layer, laminating the wafer for theactive layer through the oxide film to a wafer for a support substrate,and then exfoliating the wafer for the active layer at the hydrogen ionimplanted layer (first invention).

(2) A method of producing a semiconductor substrate, which comprisesforming an oxide film having a thickness of not more than 50 nm on awafer for an active layer forming a silicon layer, implanting ions otherthan hydrogen into the wafer for the active layer to a positionshallower than an exfoliation region of the wafer for the active layer,implanting hydrogen ions into the exfoliation region to form a hydrogenion implanted layer, laminating the wafer for the active layer throughoxide film to a wafer for a support substrate, and then exfoliating thewafer for the active layer at the hydrogen ion implanted layer (secondinvention).

(3) A method of producing a semiconductor substrate according to item(1) or (2), wherein a plasma treatment is carried out prior to thelamination of the wafer for the active layer and the wafer for thesupport substrate.

According to the invention, the semiconductor substrate formed bydirectly silicon wafers to each other through the oxide film having athickness thinner than the conventional one or without forming the oxidefilm can be produced under a stable quality without causing defects suchas voids or blisters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing procedures of producing a semiconductorsubstrate by the conventional lamination process;

FIG. 2 is a graph showing a hydrogen dose and a thickness range of anoxide film for obtaining a good product;

FIG. 3 a flow chart showing procedures of producing a semiconductorsubstrate according to the invention;

FIG. 4 is a graph showing a relation between atomic mass of each elementand a ratio of oxygen atom recoiled to the each element ion in theelement implantation;

FIG. 5 is a graph showing adequate implantation doses of argon ions andoxygen ions; and

FIG. 6 is a flow chart showing procedures of producing a semiconductorsubstrate according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention lies in that when a semiconductor substrate is produced bydirectly silicon wafers to each other through the oxide film having athickness thinner than the conventional one or without forming the oxidefilm, in addition to hydrogen ions for exfoliating the wafer for theactive layer, ions other than hydrogen ions are implanted to sputter anecessary quantity of oxygen from the oxide film and implant oxygen intothe active layer, and concrete methods therefor are explainedindividually.

In the method according to the first invention shown in FIG. 3, a wafer1 for an active layer and a wafer 2 for a support substrate arepreviously provided (step (a)), and an oxide film 3 is formed on thewafer 1 for the active layer (step (b)), and then hydrogen ions areimplanted into the wafer 1 for the active layer to form an ion implantedlayer 4 in the interior of the wafer 1 for the active layer (step (c)).

Thereafter, ions other than hydrogen such as oxygen ions or argon ionsare implanted to a position that a depth from the surface side thehydrogen ion implantation is shallower than the hydrogen ion implantedlayer 4 (step (d)). When the implantation of oxygen ions or argon ionsis carried out together with the implantation of hydrogen ions, theseions sputter oxygen from the oxide film to implant oxygen required forsuppressing void or blister defects into the active layer.

Then, the wafer 1 for the active layer is laminated through the oxidefilm 3 at the ion implanted side to the wafer 2 for the supportsubstrate (step (e)), and the exfoliation heat treatment is conducted topartly exfoliate the wafer 1 for the active layer at the ion implantedlayer 4 as a cleavage plane (exfoliation face) (step (f)), andthereafter re-oxidation treatment (step (g)), removal of oxide film(step (h)) and planarization treatment (step (i)) are carried out toproduce a semiconductor substrate 7 in which a silicon layer 6 is formedon a buried oxide film 5.

As the planarization treatment is suitable a treatment in Ar or H₂atmosphere at a high temperature above 1100° C.

In the above method, the ions other than hydrogen are particularlyimplanted at the step (d) in addition to the implantation of hydrogenions at the precedent step, so that the diffusion of hydrogen into thelaminated interface at the exfoliation heat treatment of the step (f) issuppressed by oxygen sufficiently sputtered at these steps to suppressthe occurrence of voids or blisters, whereby there is obtained thesemiconductor substrate having a thin thickness of the oxide film.

The condition for implanting oxygen required for the suppression of voidor blister defects in the active layer by conducting the implantation ofoxygen ions or argon ions in addition to the implantation of hydrogenions to sputter oxygen from the oxide film with these ions is explainedin detail below.

In order that N_(D) defined in the above equation (I) satisfiesN_(D)>4.2×10¹⁴ atoms/cm² through the implantation of ions other thanhydrogen, it is necessary that a shortage of N_(HO) (oxygen introducedinto the active layer by hydrogen ion implantation) is made up by N_(IO)(oxygen introduced into the active layer by element(s) other thanhydrogen) and N_(ID) (defects introduced into the active layer byimplanting ions other than hydrogen).

There are B, P and As as an element generally implanted into the wafer.In Table 1 is shown a dose of oxygen introduced by a recoil phenomenonin the implantation of such an element ion. In FIG. 4 are shown resultsarranged as a relation between atomic mass of each element and a ratioof oxygen atom recoiled in the implantation of the element to theelement ion (recoil ratio). The recoil phenomenon means a phenomenonthat when the element ion is implanted through the oxide film, oxygenatom is sputtered from the oxide film by the implanted ion to strikeinto Si crystal.

From the results of FIG. 4, a recoil ratio R_(Z) of a certain elementcan be represented by the following equation (III):R _(Z)=0.0007×q _(Z) ^(1.325)  (III)where q_(Z) is an atomic mass.

TABLE 1 Thickness of oxide film: 1 nm, Ion dose: 1.00 × 10¹³ atoms/cm²Recoiled oxygen Oxygen concentration Atomic atom/implanted introduced byrecoil Element mass element ion phenomenon B 11 0.0150 1.50 × 10¹⁸ P 310.0680 6.80 × 10¹⁸ As 75 0.1900 1.90 × 10¹⁸

Each recoil ratio of hydrogen, oxygen and argon is determined accordingto the equation (III) as follows:

Hydrogen: R_(H)=0.0007 (q_(H)=1)

Oxygen: R_(O)=0.0277 (q_(O)=16)

Argon: R_(Ar)=0.0934 (q_(Ar)=40)

When argon ions are implanted after the hydrogen ion implantation athydrogen dose: 6×10¹⁶ atoms/cm² and implantation energy: 50 keV, arelation between implantation dose of argon ions and thickness of oxidefilm is determined in order that N_(D) defined in the equation (I)satisfies N_(D)>4.2×10¹⁴ atoms/cm².

At first, the equation (I) in the implantation of argon ions isrepresented as follows:N _(D) =N _(HO) +N _(IO) +N _(ArD)  (I)When N_(HO), N_(ArO) and N_(ArD) areN _(HO) =D _(H)(hydrogen dose)×t _(box)(thickness of oxide film)×k_(HO)(coefficient)  (II)(where D_(H)=6×10¹⁶ atoms/cm² and k_(HO)=4.76×102 8/cm)),N _(ArO) =D _(Ar)(argon dose)×t _(box)(thickness of oxide film)×k_(ArO)(coefficient)(where k_(ArO)=R_(Ar)/R_(H)×k_(HO)=0.0934/0.0007×4.67×10²=6.23×10⁴) andN_(ArD)=D_(Ar), the above equation (I) isN_(D)=N_(HO)+N_(ArO)+N_(ArD)=D_(H)×t_(box)×k_(HO)+D_(Ar)×t_(box)×k_(ArO)+D_(Ar)=4.2×10¹⁴atoms/cm², from which the implantation dose of argon ions isD_(Ar)=(4.2×10¹⁴−6.0×10¹⁶×t_(box)×4.67×10²)/(t_(box)×6.23×10⁴+1).

Similarly, when oxygen ions are implanted after the hydrogen ionimplantation at hydrogen dose: 6×10¹⁶ atoms/cm² and implantation energy:50 keV, a relation between implantation dose of oxygen ions andthickness of oxide film is determined in order that N_(D) defined in theequation (I) satisfies N_(D)>4.2×10¹⁴ atoms/cm².

At first, the equation (I) in the implantation of oxygen ions isrepresented as follows:N _(D) =N _(HO) +N _(OO) +N _(OD)  (I)When N_(HO), N_(OO) and N_(OD) areN _(HO) =D _(H)(hydrogen dose)×t _(box)(thickness of oxide film)×k_(HO)(coefficient)  (II)(where D_(H)=6×10¹⁶ atoms/cm² and k_(HO)=4.76×10² (/cm)),N _(OO) =D _(O)(oxygen dose)×t _(box)(thickness of oxide film)×k_(OO)(coefficient)(where k_(OO) =R _(O) /R _(H) ×k _(HO)=0.0277/0.0007×4.67×10²=1.85×10⁴)and N_(OD)=D_(O), the above equation (I) isN_(D)=N_(HO)+N_(OO)+N_(OD)=D_(H)×t_(box)×k_(HO)+D_(O)×t_(box)×k_(OO)+D_(O)=4.2×10¹⁴atoms/cm², from which the implantation dose of oxygen ions isD_(O)=(4.2×10¹⁴−6.0×10¹⁶×t_(box)×4.67×10²)/(t_(box)×1.85×10⁴+1).

In FIG. 5 are shown results obtained by arranging the above adequateimplantation doses of argon ions and oxygen ions by the thickness of theoxide film. Although defects are introduced into the active layer byimplanting the argon ions or oxygen ions, if the implantation dose istoo large, the crystallinity of the active layer is broken and the goodactive layer is not obtained. From such a viewpoint, there is the upperlimit on the implantation doses of argon ions and oxygen ions in FIG. 5.The upper limit is experimentally 1×10¹⁶ atoms/cm² in case of the argonions and 2×10¹⁶ atoms/cm² in case of the oxygen ions, respectively.

In the method according to the second invention shown in FIG. 6, a wafer1 for an active layer and a wafer 2 for a support substrate arepreviously provided (step (a)). Firstly, an oxide film 3 is formed onthe wafer 1 for the active layer (step (b)), and ions other thanhydrogen such as oxygen ions or argon ions are implanted into the wafer1 for the active layer up to a position shallower than an exfoliationregion of the wafer 1 for the active layer (step (c)). Thereafter,hydrogen ions are implanted into the exfoliation region to form ahydrogen ion implanted layer 4 (step (d)).

Since the implantation of oxygen ions or argon ions is carried out inaddition to the implantation of hydrogen ions, oxygen is sputtered fromthe oxide film by these ions to implant oxygen required for thesuppression of void or blister defects into the active layer.

Then, the wafer 1 for the active layer is laminated through the oxidefilm 3 at the ion implanted side to the wafer 2 for the supportsubstrate (step (e)), and an exfoliation heat treatment is applied topartly exfoliate the wafer 1 for the active layer at the ion implantedlayer 4 as a cleavage plane (exfoliation face) (step (f)), andthereafter re-oxidation treatment (step (g)), removal of oxide film(step (h)) and planarization treatment (step (i)) are carried out toproduce a semiconductor substrate 7 in which a silicon layer 6 is formedon a buried oxide film 5.

In the above method, the ions other than hydrogen are particularlyimplanted at the step (c) in addition to the hydrogen ion implantationat the subsequent step, so that the diffusion of hydrogen into thelaminated interface at the exfoliation heat treatment of the step (f) issuppressed by oxygen sufficiently sputtered at these steps to suppressthe occurrence of voids or blisters, whereby there is obtained thesemiconductor substrate having a thin thickness of the oxide film.

Even in the method of FIG. 6, it is preferable to conduct theimplantation of argon ions or oxygen ions within the preferable rangeshown in FIG. 5.

In any methods shown in FIGS. 3 and 6, it is preferable to conduct aplasma treatment for increasing the adhesion strength at the laminatedinterface prior to the lamination between the wafer 1 for the activelayer and the wafer 2 for the support substrate. Since the plasmatreatment has effects of activating the laminated surface and removingorganic substance adhered to the surface, the adhesion strength of thelaminated interface is improved to bring about the decrease of voids orblisters. Moreover, the conditions of the plasma treatment are notparticularly limited, but the similar effects can be typically developedby treating the wafers in a gas atmosphere of oxygen, nitrogen, hydrogenor the like for several tens seconds.

Comparative Example 1

According to the method shown in FIG. 1, a laminated semiconductorsubstrate is prepared by forming an oxide film of 150 nm in thickness onthe surface of the wafer for the active layer, implanting hydrogen ionsso as to come a peak of the implantation dose (ion implanted layer) to adepth position of 500-nm from the surface of the wafer for the activelayer, and then laminating the wafer for the active layer to the waferfor the support substrate and conducting the exfoliation heat treatmentto exfoliate the wafer for the active layer at the hydrogen ionimplanted peak region (ion implanted layer), and thereafter conductingan oxidation treatment and removing the oxide film and conducting theplanarization treatment.

Comparative Example 2

According to the method shown in FIG. 1, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 nm in thickness onthe surface of the wafer for the active layer, implanting hydrogen ionsso as to come a peak of the implantation dose (ion implanted layer) to adepth position of 500 nm from the surface of the wafer for the activelayer, and laminating the wafer for the active layer to the wafer forthe support substrate and conducting the exfoliation heat treatment toexfoliate the wafer for the active layer at the hydrogen ion implantedpeak region (ion implanted layer), and thereafter conducting anoxidation treatment and removing the oxide film and conducting theplanarization treatment.

Comparative Example 3

According to the method shown in FIG. 1, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 nm in thickness onthe surface of the wafer for the active layer, implanting hydrogen ionsso as to come a peak of the implantation dose (ion implanted layer) to adepth position of 500 nm from the surface of the wafer for the activelayer, and then subjecting the surfaces of the wafer for the activelayer and the wafer for the support substrate to an oxygen plasmatreatment and laminating the wafer for the active layer to the wafer forthe support substrate and conducting the exfoliation heat treatment toexfoliate the wafer for the active layer at the hydrogen ion implantedpeak region (ion implanted layer), and thereafter conducting anoxidation treatment and removing the oxide film and conducting theplanarization treatment.

Invention Example 1 First Invention

According to the method shown in FIG. 3, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 mm in thickness onthe surface of the wafer for the active layer, implanting hydrogen ionsso as to come a peak of the implantation dose (ion implanted layer) to adepth position of 500 nm from the surface of the wafer for the activelayer, and further implanting oxygen ions so as to come a peak of theimplantation dose to a depth position of 50 nm from the surface of thewafer for the active layer, and laminating the wafer for the activelayer at its ion implanted side to the wafer for the support substrateafter both the ion implantations, and conducting the exfoliation heattreatment to exfoliate the wafer for the active layer at the hydrogenion implanted peak region (ion implanted layer), and thereafterconducting an oxidation treatment and removing the oxide film andconducting the planarization treatment.

Invention Example 2 First Invention

According to the method shown in FIG. 3, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 nm in thickness onthe surface of the wafer for the active layer, implanting hydrogen ionsso as to come a peak of the implantation dose (ion implanted layer) to adepth position of 500 nm from the surface of the wafer for the activelayer, and further implanting argon ions so as to come a peak of theimplantation dose to a depth position of 50 nm from the surface of thewafer for the active layer, and laminating the wafer for the activelayer at its ion implanted side to the wafer for the support substrateafter both the ion implantations, and conducting the exfoliation heattreatment to exfoliate the wafer for the active layer at the hydrogenion implanted peak region (ion implanted layer), and thereafterconducting an oxidation treatment and removing the oxide film andconducting the planarization treatment.

Invention Example 3 Second Invention

According to the method shown in FIG. 6, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 nm in thickness onthe surface of the wafer for the active layer, implanting oxygen ions soas to come a peak of the implantation dose to a depth position of 50 nmfrom the surface of the wafer for the active layer, and furtherimplanting hydrogen ions so as to come a peak of the implantation dose(ion implanted layer) to a depth position of 500 nm from the surface ofthe wafer for the active layer, and laminating the wafer for the activelayer at its ion implanted side to the wafer for the support substrateafter the implantation of both the ions, and conducting the exfoliationheat treatment to exfoliate the wafer for the active layer at thehydrogen ion implanted peak region (ion implanted layer), and thereafterconducting an oxidation treatment and removing the oxide film andconducting the planarization treatment.

Invention Example 4 Second Invention

According to the method shown in FIG. 6, a laminated semiconductorsubstrate is prepared by forming an oxide film of 20 nm in thickness onthe surface of the wafer for the active layer, implanting argon ions soas to come a peak of the implantation dose to a depth position of 50 nmfrom the surface of the wafer for the active layer, and furtherimplanting hydrogen ions so as to come a peak of the implantation dose(ion implanted layer) to a depth position of 500 nm from the surface ofthe wafer for the active layer, and laminating the wafer for the activelayer at its ion implanted side to the wafer for the support substrateafter the implantation of both the ions, and conducting the exfoliationheat treatment to exfoliate the wafer for the active layer at thehydrogen ion implanted peak region (ion implanted layer), and thereafterconducting an oxidation treatment and removing the oxide film andconducting the planarization treatment.

Invention Examples 5-8

In these examples, the same procedures as in Invention Examples 1-4 arerepeated, respectively, except that the surfaces of the wafer for theactive layer and the wafer for the support substrate are subjected to anoxygen plasma treatment prior to the lamination between the wafer forthe active layer and the wafer for the support substrate. Moreover, theplasma treatment is carried out under condition that the wafers are keptfor 20 seconds after the interior of the reaction chamber replaced withoxygen gas is rendered into a vacuum state.

With respect to the thus obtained semiconductor substrates, the defectnumber is visually measured under a high-intensity light-gathering lampor a fluorescent lamp. The results are shown in Table 2. As seen fromTable 2, the occurrence of defects is suppressed in the semiconductorsubstrates according to the invention even when the buried oxide film isthin or the oxide film is not existent. Moreover, it is preferable topreviously implant ions other than hydrogen because when hydrogen ionsare previously implanted, the organic substance existing on the surfaceof the wafer is liable to be fixed on the wafer to fear the occurrenceof the blisters. More preferably, the wafer after the implantation ofions other than hydrogen is cleaned to conduct the hydrogen ionimplantation.

TABLE 2 Ion Ion Defect Thickness implan- implan- number of oxide tationtation Plasma (defects/300 film (nm) 1 2 treatment mm wafer) Comparative150 H — — not more Example 1 than 2 Comparative 20 H — — 50 Example 2Comparative 20 H — ◯ 30 Example 3 Invention 20 H O — not more Example 1than 10 Invention 20 O H — not more Example 2 than 2 Invention 20 H Ar —not more Example 3 than 10 Invention 20 Ar H — not more Example 4 than 2Invention 20 H O ◯ not more Example 5 than 5 Invention 20 O H ◯ not moreExample 6 than 1 Invention 20 H Ar ◯ not more Example 7 than 5 Invention20 Ar H ◯ not more Example 8 than 1

1. A method of producing a semiconductor substrate, which comprises thesteps of: forming an oxide film having a thickness of not more than 50nm on a wafer for an active layer, wherein the wafer has a surface sideon which, a silicon layer is formed as the active layer; implanting ionsother than hydrogen into the wafer for the active layer to a positionshallower than an exfoliation region of the wafer for the active layer,implanting hydrogen ions into the exfoliation region to form a hydrogenion implanted layer, laminating the wafer for the active layer throughthe oxide film to a wafer for a support substrate, and then exfoliatingthe wafer for the active layer at the hydrogen ion implanted layer;wherein the implanting of ions other than hydrogen is conducted tosputter a first quantity of oxygen from the oxide film; wherein theimplanting of hydrogen ions is conducted to sputter a second quantity ofoxygen from the oxide film; wherein the hydrogen ions are implantedafter the implanting of ions other than hydrogen; wherein the firstquantity of oxygen and the second quantity of oxygen are determined inconsideration of total factor number producing an effect of suppressinghydrogen diffusion (N_(D)) expressed by formula (I) and N_(ID) asfollows:N _(D) =N _(HO) +N _(IO) +N _(ID)  (I) wherein N_(D): total factornumber producing an effect of suppressing hydrogen diffusion, N_(HO):oxygen introduced into the active layer through hydrogen ionimplantation, N_(IO): oxygen introduced into active layer through ionimplantation other than hydrogen, N_(ID): defects introduced into activelayer through ion implantation other than hydrogen, andN _(D)>4.2*10¹⁴ atoms/cm².
 2. A method of producing a semiconductorsubstrate according to claim 1, wherein a plasma treatment is carriedout prior to the lamination of the wafer for the active layer and thewafer for the support substrate.